Viable Strategy for Suppressing Antisite Defects and Band Tailing States in Solution-Processed Kesterite Solar Cells via IIIA Incorporation: Case of Aluminum

Suppressing the CuZn antisite defects and band tailing states is paramount for Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. To this end, cation doping has been widely adopted and investigated. Nevertheless, to the best of our knowledge, there is a scarcity of reports specifically addressing the doping of group IIIA elements to date. Herein, we present a viable strategy, incorporating the Al element, to achieve superior absorber quality and device performance. The addition of Al-doping not only improves the selenization degree but also enhances surface smoothness and induces a more Cu-deficient CZTSSe surface, thereby elevating both the quality of the absorber and heterojunction interface. Furthermore, we observe that the CuZn defect can be effectively mitigated through the substitution of Al dopants at the Zn site, consequently resulting in a reduction of band tailing states. Consequently, it significantly improves the efficiency from 6.24 to 9.25% with a low open-circuit voltage deficit of ∼0.291 V relative to the doping-free case, one of the highest values for the type of IIIA element doping cells. Our results demonstrate that Al incorporation is also a feasible pathway to suppress the antisite defects and band tailing states in solution-processed CZTSSe, thereby facilitating the realization of efficient kesterite solar cells.